This invention relates to the formulation of artemisinin derivative (Dihydroartemisinin) for the emergent treatment and control of uncomplicated/severe complicated/cerebral and multi-drug resistance malaria. Dihydroartemisinin is a lactol derivative of artemisinin (Qinghaosu), the principle antimalarial constituent of the plant Artemisia annua. 
Malaria is caused by blood protozoa of the genus Plasmodium. The four species of Plasmodium that infect humans are Plasmodium vivax, P. malariae, P. ovale and P. falciparum, the last one is responsible for producing severe complications and cerebral malaria, which can cause the patient to lapse into a coma and ultimately leads to death. In many parts of the world, strains of P. falciparum have emerged which are resistant to chloroquine, mefloquine, halofantrinc, quinine and sulfadoxin+pyrimethamine combination, and sulfa methodpyrazine+pyrimethamine combinations the trusted drugs of choice for control of malaria. Like-wise P. vivax infections resistant to chloroquine are emerging in different countries. More than 270 million people suffer from the disease, and 1.2-1.7 million deaths occur yearly. Mortality is more among children under 5 years of age who are specially sensitive because of their lack of immunity to the disease (Ziffer H; Highet RJ and Klayman DL; Artemisinin an endoperoxide antimalarial from A. annua. Progress in the chemistry of organic natural product: Herz W (Ed.). Springer-Wien New York, 1997. P. 121-214).
Severe complicated malaria is a life-threatening condition and comatose cerebral malaria cases need emergency parental therapy. Severe P. falciparum infections are common in both rural and urban areas and the management of these cases becomes difficult because of emerging problems of drug resistant infections. The comatose cases generally do not survive more than 72 hrs and therefore, require urgent antimalarial drug therapy. The suppository preparations of a variety of antimalarials can be effectively used as emergency treatment in rural areas as well as primary health care centres and these can be easily administered even by unskilled health workers in remote areas. Several reports have been published which support the observation that rectal suppository preparations of artemisinin have powerful effect in reducing the falciparum parasitaemia in critically sick and severe cases including cerebral complications (Vinh et al. (1997); Trans Roy Soc. Trop. Med. Hyg. 91, 465-467; Li et al 1985. J Trad. Chinese Med. 5, 159-161).
The endoperoxides are a promising class of antimalarial drugs which may beet the dual challenges posed by drug parasites and the rapid progression of severe malarial illness and complications which can prove fatal unless emergency treatment is instituted. Artemisinin, is a sesquiterpene lactone containing an endoperoxide bridge (xe2x80x94Oxe2x80x94Oxe2x80x94C) and is unique among the antimalarial drugs. Dihydroartemisinin (DHA) is the reduced lactol derivative of artemisinin and the semisynthetic derivatives (artemether, arteether, artesunate and artelinate) are ethers or esters of the lactol. In general, the endoperoxides present in all these derivatives, have several advantages over existing antimalarial drugs. These derivatives show little or no cross-resistance to existing anitmalarials. The endoperoxides are fast-acting and clear the periphera blood of parasites more rapidly than other available drugs and finally resistance to the endoperoxides has not yet developed, despite widespread clinical trials. (White N.J., 1994, Artemisinin Current Status: Trans R. Soc. Trop Med Hyg. (88 Suppl). 53-54). The attractive feature of the drugs (arteether, artemether) is the lack of systemic neurotoxicity at the clinically prescribed doses (Looaresuwan, S. et al. 1997 Acta. Tropica. 67, 197-205).
Prior art
Dihydroartemisinin (DHA) is the simplest semisynthetic derivative of Artemisinin, the principle antimalarial constituent of medicinal plant Armeisia annua (Warburton, D. (1984) Handbook of Experimental Pharmacology, MaCmillan NY pp. 471-495; Hoffman, S. L. (1986). Clin. Trop. Med. Communicable Dis. 1, 171-274). It has considerable activity in vivo and in vitro and is 3.8 to 5 times more potent than artemisinin (de Vries, P. et al (1996). Drugs 52, 818-836; China Cooperative Research group on Qinghaosu, (1982b) J. Trad. Chin. Med. 2, 17-24); Gu, H. M. et al, (1984) Trans. Roy. Soc. Trop. Med. Hyg, 78, 265-270). In vitro bioassay against drug-resistant P. falciparum cultures (W-2 Indo-China and D-6 Sierre Lone strains) showed that direct antimalarial activity of DHA is superior to that of artemether and arteether xcex2 (Lin, A. J. et al (1987) J. Med. Chem. 30, 2147-2150). However, because of its poor solubility in water, DHA had only been formulated as an oral preparation (Tablet) (Li, Q. G. et al (1998) J. Pharm. Pharmacol. 50, 173-182). DHA has been chiefly used for making semisynthetic derivatives such as artemether (AM) and arteether (AE) which are soluble in oil, and the water soluble drug artesunate (AS) (Luo, X. et al, (1984) Helv. Chem. Acta. 67, 1515-1522; Lin, A. J. et al, (1987) J. Med. Chem. 30, 2147-2150; Brossi, A. et al, (1988) J. Med. Chem. 31, 645-650). Zhao and Song (1993 Yao Hsuch Pao, 28, 342-346) compared the pharmacokinetics of oral dihydroartemisinin (DHA) and qinghaosu (QHS) Tablets in human volunteers and reported very high bioavailability of DHA (oral tablets) as compared to QHS (oral) and serum level after QHS were only 1.6-10.8% that of oral DHA preparation. For oral administration DHA was reported to be far superior blood schizontocide compared to QHS. Qi-Gui Li et al (1998 J. Pharm. Pharmacol. 50, 173-182) compared the oral bioactivity of dihydroartemisinin (DHA) with artemether, arteether and artesunic acid in rats and concluded that maximum plasma concentration was produced by oral DHA (769xc2x1218) in comparison to artemether (381xc2x1113), arteether (324xc2x110) and artesunic acid (208xc2x125 ng mlxe2x88x921). Further area under plasma concentration time curve (ngh mlxe2x88x921) was highest with oral DHA 9615xc2x156) as compared to artemether (306xc2x152), arteether (298xc2x168) and artesunic acid (217xc2x134). Elimination half life (h) was longer for DHA (4.94xc2x10.73) as compared to artemether (2.04xc2x10.18), arteether (1.79xc2x10.47) and artesunic acid (1.34xc2x126 h). DHA was reported to be active metabolite of other artemisinin derivatives such as artemether (AM), arteether (AE), Artesunate (AS) Artelinic acid (AL).
Benakis et al (1996) administered (60 mg dose representing half of daily dose) oral dihydroartemisinin tablets to six uncomplicated falciparum malaria cases and the peak plasma levels of dihydroartemisinin (0.26-0.71 xcexcg/ml) were recorded between 1‥2 hrs in four subjects. Thereafter, plasma level dropped and there was complete excretion by 6 hrs. Elimination half-life of DHA was 0.71-1.45 h, drug was well tolerated in 2 subjects while 4 subjects experienced mild headache, nausea or vomiting. One subject showed gastrointestinal hemorrhage and stupor 30 min after drug (Tablet) administration. Benakis et al (1996 J. Trop. Med. Hyg. 24, Suppl 1, 7-11) suggested that the development of a sustained release form of DHA could overcome the adverse drug reaction of table form of drug.
Benakis et al (1977) also reported that following oral artesunate administration, the maximum dihydroartemisinin, plasma level produced was much higher 0.57xc2x10.18 xcexcg/ml compared to that of parent compound artesunate which recorded peak level of 0.12xc2x10.11 xcexcg/ml. It may be emphasized, that DHA level was 5-fold higher compared to that of artesunate and that DHA is the main antimalarial principle following artesunate administration. Further it was pointed out that for artesunate type of antimalarials, dose administration (every 3 hourly) would be necessary because of a very short half-life of the drug. However, Bethell et al (1977 Trans R. Soc. Trop. Med. Hyg. 91, 195-198) had observed wide variation in peak plasma concentration of DHA (664 ng of DHA/ml, 95/Cl 387-9410, range (79-1394) in Vietnamese P. falciparum cases who were administered oral artesunate.
The initial studies with artemisinin suppositories were carried out in China for the control of P. falciparum. The suppository treatment was found satisfactory as shown by fever clearance time (15-39 h) and parasite clearance time (35-52 h) (Li et al, 1989, IV World Cong. Clin. Pharmacol. and Therapeutics, Munnich-Heidel-berge, Germany, July 1989). Arnold et al (1990; Trans Roy. Soc. Trop. Med. Hyg. 85, 499-502) reported that artemisinin suppositories (Containing 2800 mg total drug administered in 56 h) produced complete parasite clearance in 41.8 h in cases with acute P. falciparum infection, while those receiving quinine (Oral) at 1500 mg dose dailyxc3x9714 days would take 68.1 for parasite clearance.
Hien et al (1991 Trans. Roy. Soc. Trop. Med. Hyg. 84, 499-502) had reported that artemisinin (600-2200 mg) suppositories rapidly cleared asexual P. Falciparum parasites in children and confirmed the problem of high incidence recrudescence with this drug. Suppositories could be used as presumptive treatment to prevent the development of high parasitaemia. In the study 10 children receiving 10-mg/kg artemisinin took 18.9xc2x14.7 hrs to achieve initial 95% clearance of parasitaemia.
Astesunate suppositories (1600 mg dose administered over 3 days) were evaluated by Looareesuwan et al (1997, Am J. Trop. Med. Hyg. 57, 348-53) and (200 mgxc3x973 days) by Kyaw et al. 1996. According to these workers, the artesunate suppositoreis achieve complete parasite clearance at a fantastic speed (16-36 h) as good as that achieved by oral tablet of artesunate. Patients with cerebral symptoms and altered conscious levels generally give a good response and recover. Rectal suppositories were able to control severe complications of P. falcipurum cases better than im artemether as shown by time to regain full consciousness in comatose cases.
Artemisinin suppository treated cases look 24 (18-30) h for recovery from coma, while artemether took 47 h (31-63 h). The efficacy of rectal artemisinin suppository was equal to iv artesunate which is considered to be most fast-acting treatment for comatose cases as reported by Hein et al. (1992). The development of rectal formulation would provide a better alternative to the oral treatment in terms of quick absorption, high bio-availability and effective plasma level adequate to exert antimalarial effect in the blood.
The fast excretion rate would justify the repeated rectal administration every 4 hrs initially to control severe complicated infections, without causing any toxicity. Rectal suppository are simple to administer, easy to store at room temp and its administration does not require any special equipment, and can be given as emergency drug at rural health centres throughout the developing world where malaria related mortality is high.
The water soluble derivative of DHA, namely the artesunate acid has been found to be very effective against malaria in vitro and has got low toxicity in vivo and in vitro (Yang, Q. et al (1982) J. Trad. Chin. Med., 3, 99-103; Lin, A. J. et al (1987) J. Med. Chem. 30, 2147-2150). Although Artesunate (AS) is 3.2 time more potent than artemisinin and is less toxic than artemether, it has limited stability in solution (Zhou, Z. M. et al (1987) J. Chromato 414, 77-90; Panisko, M. D. and Keystone, J. S. (1990) Drugs, 39, 160-189) and dose must be prepared immediately before administration. Pharmacokinetic data obtained in man, rabbit, rat and dog suggested that artesunic acid is distributed and hydrolysed to DHA by plasma esterase with an elimination half-life of 2-4 min in rabbits and 27 min in dogs (Zhao, K. C. et al (1986) Acta. Pharm. Sin. 21, 736-739). Due to its rapid and extensive conversion to DHA, artesunic acid could be considered a prodrug of DHA (Titulaer, H. A. C. et al, Int. J. Pharm. 69, 83-90,1991). The pharmacodynamic activity of artesunate is due to the metabolite (DHA) rather than to be administered product.
Karbwang, J. et al (1998) (Ann. Trop. Med. and Parasitol, 92, 31-36) studied the pharmacokinectics of artemether (oral) and its conversion to DHA in P. falciparum cases and concluded that DHA was believed to be the main determinant of the successful treatment, suggesting that anitmalarial activity corresponded to DHA level in plasma. Plasma level of DHA metabolite was nearly three fold higher in patients with sensitive P. falicparum infection. The mean ratio of inhibitory activities of artemether vs. DHA against P. falciparum isolates in Thailand was 1:2.9 within 6-12 hrs, the plasma artemether levels decreased fast, while DHA level was still higher. However, both artmether and artesunate are susceptible to breakdown by humidity, light and acidic conditions at room temperature. An aqueous solution of sodium artesunate at pH 7-8 hydrolyses within 1 h to DHA.
DHA is a major metabolite of artemether, arteether and artesunic acid/artesunate in vivo (de Vriens, P. J. and Dien, T. K. (1996) Drugs, 52, 181-836; Chi, H. T. et al (1991) Biol Mass Spectrum 20, 609-628; Zhou, Z. M. et al (1987) J. Chromatog, 414, 77-90; Li, Q. G. (1998) J. Pharm. Pharmacol. 50, 173-182). The high rate of malaria recrudescence associated with other artemisinin derivatives has been ascribed at least partly to short plasma half-life.
The pharmacodynamic activity of artemether in healthy adults was reported to be due to the metabolite DHA rather than administered prodrug. The main metabolite DHA is approximately three times as active as the parent compound in terms of antimalarial activity against P. falicparum (Teja-Isavadharm, P. et al (1996) Br. J. Clin. Pharmacol. 42, 599-604). The contribution of other unidentified metabolites to antimalarial activity was reported to be negligible ((Lee, I. S. and Heefford, C. D. (1990) Pharmacol Ther.48, 345).
In vivo conversion of arteether (AE), artemether (AM) and artesunate (AS) to DHA in rats was compared via all the three routes (oral, im and rectal) of administration, and the conversion rate was faster with AS followed by AE and AM. The high conversion of AS to DHA can be explained by the fact that AS and DHA show same in vitro antimalarial potency against chloroquine sensitive and chloroquine resistant strains of P. bergei. Although the DHA level obtained after dosing with AM, AE and AS were less than 2.6% those after im dosing with DHA, the high antimalarial activity of DHA probably contributes significantly to overall antimalarial activity of these drugs in vivo (Li, Q. G. et al (1998) J. Pharm. Pharmacol, 50,173-182).
The bio-availablility of artemether in healthy subjects given drugs by intramuscular and intra-rectal routes showed that plasma profile of its active metabolite dihydroartemisinin following intarcctal (ir) administration suggested that this route should be assessed as an alternative to intramuscular route in the rural tropics (Teja Isavadharm et al. 1996. Br. J. Clin. Pharmacol. 42, 599-604). The conversion of artesunate to its active metabolite dihydroartemisinin appears unique in antimalarial pharmacology because of its rapid clearance rate. (Benthell et al. b1998, Br. J. Clin Pharmacol. 45, 123-129).
The im bio-availability of AM and AE were very low, indicating incomplete absorption of these drugs atleast during first 8 h after im administration. The bio-availability of DHA on the other hand, is midway between other oil soluble drugs and water soluble drugs. The relatively slow and incomplete bio-availablity of both 1M and oral preparation of artemether is of some concern as this is a front line treatment for severe and complicated falciparum malaria. The im absorption of artemether in children with severe malaria (Cerebral malaria (CM) accompanied with respiratory distress was reported to be erratic and five CM cases did not show plasma DHA levels in one study (Murphy, S. A. et al.(1997) Trans. Roy. Soc. Trop. Med. Hyg. 91, 332-334). In view of the impaired absorption of artemether in children, there is an urgent need to develop an effective antimalaria for children. Oral artemether has been reported to undergo inadequate drug absorption in P. falciparum cases which resulted in recrudescence (Bangchang, K. N. A. et al (1994) J. Chem. Pharmac. 37, 249-253). Clinical investigators therefore, advocate the replacement of artemether with iv artesunate preparation for treatment of severe malaria in children (Murphy, S. A. et al (1997) Trans. Roy Soc. Trop.Med. Hyg. 91, 332-334).
The plasma level of DHA by im route were sustained over 30 hr and parasitidal effect was maintained for much longer time period compared to oral or Intarectal route (DHA activity by im route, AUC 3445 n Mlo lxe2x88x921 h compared to oral route 3855 n molxe2x88x921 h but activity due to DHA was prolonged beyond 30 h while the oral dose provided effective level upto 10 h (Teja-Isavadharm, P. et al (1996) Br. J. Clin. Pharmacol. 42, 599-604).
The earlier work on artemisinin, arteether, artelinate, artesunate administered by im formulations and arteether and DHA administered by oral route have shown good gemetocidal activity both in animal model and against P. falciparum. These drugs have potential for the interruption malaria transmission. (Dutta, G. P. et al (1989) Chemotherapy (Bansal) 35, 2000-2007; Tripathi, R. et al (1990), Amer. J. Trop. Med. Hyg. 43, 571-575; ibid, (1985) 54, 652-654).
Cost is a critical factor in determining use of antimalarial drugs. Artemisiinin derived drugs are now available commercially in a few countries but they are restricted because of high cost, eg., oral artesunate currently cost about $5-6 per treatment as compared to $1.85 for mefloquine and 7xc2x0 C. for drugs such as chloroquine. Injectable artesunate, artemether and arteether cost even more compared to quinine injections at less than $2.0 per treatment.
There is undoubtedly a real need for an effective new antimalarial drug based on artemisinin or its semi-synthetic derivatives with improved absorption, bio-availability, high plasma drug concentration for longer duration of time and cost effectivenss for the treatment of multi-drug resistant and severe complicated/cerebral malaria.
The main object of the present invention is to develop a formulation of dihydroartemisinin for the control of wide spectrum of malaria.
Anotehr object of invention is to develop improved safe formulation, less expensive, for uncomplicated malaria infections as well as for the control of multi-drug resistant malaria and emergent treatment of severe complicated cerebral malarial infections.
Still another object of invention is to develop a formulation which will be able to stop malaria related mortality among children and adults.
The present invention is to develop an improved formulation of artemisinin derivative for the control of both uncomplicated malaria and for the emergent treatment of severe complicated and cerebral malaria cases and for the treatment of multi-drug resistant malarias. This formulation comprises preparation of artemisinin derivative in sterile, neutralized refined oil which would exert fast acting blood schizontocidal activites in adults and children and has long shelf-life. The antimalarial profile of the formulation given by different routes (rectal, intramuscular and oral) has confirmed high activity.